588
21 Diodes
21.5.11 Gunn Diodes
The Gunn diode is not really a diode and thus more appropriately called Gunn element. It allows to
generate microwave radiation in the frequency range of 1–100 GHz [1808] and beyond [1809] using
GaAs and in the THz-regime using GaN [1810]. Extracting higher harmonics, frequencies of several
100 GHz can be realized [1811, 1812].
The Gunn element relies on the negative differential resistance (NDR) occurring in semiconductors
with two valleys of different mobility such as GaAs or InP (cmp. Sect. 8.4.2). At high fields, the electrons
are scattered from the -valley into the upper valley (L-valley for most materials). Accordingly, the
Gunn element is also called transferred electron device (TED). Details on Gunn elements can be found
in [1813].
The Gunn effect was discovered by and named after J.B. Gunn [134]. The spontaneous oscillation of
current in a n-type semiconductor occurs when a sufficiently large voltage (pulse) is applied that causes
the electric field in the semiconductor to reach the NDR regime (Fig. 21.78). The applied average field
of E = 16 V/25 µ m = 6.4 kV/cm [134] is larger than the threshold field of E T = 3.2 kV/cm for NDR
in GaAs (Table 8.4).
The self-started oscillations are due the inherent instability introduced by NDR. A homogeneous
(uniform) electric field and electron distribution is unstable and a thin high-field domain with bipolar
charge distribution (Gunn domain, predicted in [764]) can develop and drift through the device. After
reaching the anode, another domain can form, causing a periodically fluctuating current. The highest
frequencies can be achieved with the so-called limited-space-charge accumulation (LSA) mode which
operates without domains. Optimal performance requires non-homogeneous doping profiles. A detailed
discussion of the various oscillation mechanisms can be found in [765, 1808, 1814].
Discussion of further microwave diode devices such as the IMPATT diode can be found in [574,
1815].
21 Diodes
21.5.11 Gunn Diodes
The Gunn diode is not really a diode and thus more appropriately called Gunn element. It allows to
generate microwave radiation in the frequency range of 1–100 GHz [1808] and beyond [1809] using
GaAs and in the THz-regime using GaN [1810]. Extracting higher harmonics, frequencies of several
100 GHz can be realized [1811, 1812].
The Gunn element relies on the negative differential resistance (NDR) occurring in semiconductors
with two valleys of different mobility such as GaAs or InP (cmp. Sect. 8.4.2). At high fields, the electrons
are scattered from the -valley into the upper valley (L-valley for most materials). Accordingly, the
Gunn element is also called transferred electron device (TED). Details on Gunn elements can be found
in [1813].
The Gunn effect was discovered by and named after J.B. Gunn [134]. The spontaneous oscillation of
current in a n-type semiconductor occurs when a sufficiently large voltage (pulse) is applied that causes
the electric field in the semiconductor to reach the NDR regime (Fig. 21.78). The applied average field
of E = 16 V/25 µ m = 6.4 kV/cm [134] is larger than the threshold field of E T = 3.2 kV/cm for NDR
in GaAs (Table 8.4).
The self-started oscillations are due the inherent instability introduced by NDR. A homogeneous
(uniform) electric field and electron distribution is unstable and a thin high-field domain with bipolar
charge distribution (Gunn domain, predicted in [764]) can develop and drift through the device. After
reaching the anode, another domain can form, causing a periodically fluctuating current. The highest
frequencies can be achieved with the so-called limited-space-charge accumulation (LSA) mode which
operates without domains. Optimal performance requires non-homogeneous doping profiles. A detailed
discussion of the various oscillation mechanisms can be found in [765, 1808, 1814].
Discussion of further microwave diode devices such as the IMPATT diode can be found in [574,
1815].